Vesicles are formed by encapsulating a volume with a thin membrane which can be composed of lipids, polymers and hybrid materials. Vesicles are important for many applications. One of the applications is for encapsulation and delivery of various species which can be for cosmetic or pharmaceuticals. Good vesicles should have 1) good stability to achieve sufficiently long shelf life for storage, and good integrity for drug delivery before reaching target sites; 2) stealth layers to provide good dispersity in aqueous solution and targeting capability; and 3) suitable fluidity for release of species encapsulated at target sites when needed.
One of the most formidable challenges in developing qualified vesicles is to address a dilemma between stability and fluidity of vesicles. Vesicles with good fluidity tend to have poor stability. For example, liposomes obtained from self-assembly of amphiphilic lipids are dynamic and feasible for species to move into and out of the vesicles. However, stability of liposomes is poor due to weak interaction among short hydrophobic lipid segments responsible for integrity of the liposomes. Even though cross-linking or formation of polymer based or silica cages may stabilize the liposomes formed, fluidity is comprised.
In comparison, structures and properties of polymer vesicles formed by self-assembly of amphiphilic copolymers may be adjusted in a wider range through tuning the chemistry, composition and molecular weight of copolymers. However, stable polymer vesicles tend to have low fluidity.
In view of the above, there remains a need to develop improved vesicles which are able to encapsulate species securely, while still being able to release the species at target sites on demand.